The truth is that all biofilms are not bad. We can even look to nature to provide fine examples of biofilms, such as fuel cells and marine engineering systems. Recently however, there has been a lot of attention on biofilm formation on contact lenses and lens storage cases. Let’s discuss.
By definition, a biofilm is an aggregate or community of microorganisms where cells adhere to each other on a surface, frequently embedded within a self-produced matrix of extra-cellular polymeric substance (slime).1,2 Scientists now know that 99% of all microbial activity in an open ecosystem occurs in biofilms.3 Biofilms permit communication among organisms with quorum sensing between species, thereby allowing for a sense in numbers. With all of this, specific organisms pass genetic material to other species.2
Dental plaque is an example of biofilm deposit on the surface of teeth. Inner ear, bladder and prostate infections, and even acne, are all examples of biofilm infections.1,3,4 The significance of biofilms is just now being fully investigated. Biofilms can grow on medical devices, such as implants, catheters, cardiac valves, intrauterine devices and contact lenses, creating an opportunity for infections to stem. In cases where microbes resist antibiotics and evade the immune system, death can occur.1,2,4
Bacterial biofilm formation on contact lenses and lens storage cases clearly poses risk for infection of the cornea and sterile corneal responses.5,6 Microorganism variability includes species/strains, gene expression and inoculum. We know that biofilms decrease the effectiveness of multipurpose disinfecting solutions. However, there are currently no FDA guidelines on biofilm disinfection. Research suggests that proper lens care and scheduled disposable lens replacement may decrease the risk of infection by reducing the buildup of bacterial biofilms in lens storage cases and contact lens surfaces.6
Yvonne Wu, Ph.D., and colleagues at the Brien Holden Vision Institute have provided some intuitive recommendations for the care of lens storage cases—including digital rubbing and rinsing; wiping the lens storage case with tissue; air-drying the case; and avoiding recapping the lens case lid after use without additional cleaning methods.5 Although recommended hygiene practices do not necessarily ensure a case free from contamination, tissue wiping alone was shown to remove a significant amount of biofilm.5,6 Another study found that air-dying biofilm for 10 hours can decrease the recovery of microorganisms.6 Rubbing and rinsing not only reduced or dislodged bacteria, but also reduced nutrients that promoted growth of bacteria.5,6
Regardless of selected cleaning routine, it is easier to remove biofilm from a smooth polypropylene case, rather than a case with ridges.6,7 However, using a silver-impregnated lens storage case likely is the best defense for reducing the potential for biofilm formation.8
Take a Step Back
As we look for new ways to help battle biofilms, it might be helpful to turn back to nature. We know that bacteria will leave the colony when there is biofilm crowding and aging. Several scientists have employed strategies using certain molecules that, when introduced into the biofilm colonies, provoke genetic and physiologic changes in the bacteria to make them disperse and return to their planktonic state.3,9
By breaking apart the scaffolding that encases the organisms, the bacteria are very susceptible to viable treatment. Cellular debris from the immune system fighting infection actually provides raw material for the biofilm-DNA, actin and histones. Using the enzyme DNase, together with negatively charged poly aspartic acid to break down the bonds that support biofilms, seems to effectively render biofilms less significant.3 In fact, research shows that this treatment reduces biofilms on contact lenses by 79.2% and reduces corneal infection in animal models by 41%.3
Incorporating the aforementioned regimen recommendations in daily practice will help reduce the chance of corneal infection from pathogenic organisms and the inflammatory changes that occur as a result of endotoxins that collect on lenses and in storage cases.
1. Rose J. Biofilms: The good and the bad. Water Quality and Health Council. 2011 Dec 2. Available at: www.waterandhealth.org/biofilms-good-bad (accessed March 2012).
2. Biofilm. Wikipedia. Available at: http://en.wikipedia.org/wiki/Biofilm (accessed March 2012).
3. New method attacks bacterial infection on contact lenses. ScienceDaily. 2011 Jan 25. Available at: www.sciencedaily.com/releases/2011/01/110125160850.htm (accessed March 2012).
4. Plaque vs. biofilm and the research that could change dentistry as we know it. Mead Family Dental. 2011 Nov 21. Available at: http://meadfamilydental.com/2011/11/plaque-vs-biofilm-and-the-research-that-could-change-dentistry-as-we-know-it (accessed March 2012).
5. Wu YT, Zhu H, Willcox M, Stapleton F. Removal of biofilm from contact lens storage cases. Invest Ophthalmol Vis Sci. 2010 Dec;51(12):6329-33.
6. McLaughlin-Borlace L, Stapleton F, Matheson M, Dart JKG. Bacterial biofilm on contact lenses and lens storage cases in wearers with microbial keratitis. J Appl Microbiol. 1998 May;84(5):827-38.
7. Wu YT, Zhu H, Willcox M, Stapleton F. The effectiveness of various cleaning regimens and current guidelines in contact lens case biofilm removal. Invest Ophthalmol Vis Sci. 2011 Jul 15;52(8):5287-92.
8. Wu YT, Zhu H, Willcox M, Stapleton F. Impact of cleaning regimens in silver impregnated and hydrogen peroxide lens cases. Eye Contact Lens. 2011 Nov;37(6):365-9.
9. The DNA files: biofilms. WSKG. 2007. Available at: h ttp://wskg.org/episode/dna-files-biofilms (accessed March 2012).